You can try check your account at www.magix.com , log-in, and see at 'my products', chek for your Movie Studio 15... from there you can redownload the installation packages.
@SeaTac you'll find the downloading FAQ and the link(s) if you click "Downloading" in the first comment (from Nick Hope) in this thread. Read also at least points 9, 10, and 11 in the main FAQ, the link is in set's first post.